1. Field of the Invention
The present invention relates to control mechanisms for operating internal combustion engines and electric motors that are utilized in combination as a hybrid drive.
2. Description of Related Art
The combined use of electrical machines and internal combustion engines in a hybrid drive makes a higher level of efficiency possible when moving vehicles, as well as flexible adaptation of the operating modes of the drive unit to the desired driving mode. In particular, a hybrid drive allows efficient use of the internal combustion engine by storing electrical energy which has been obtained via the electrical machine as a generator, as well as by recovering kinetic energy when decelerating.
On the one hand, in hybrid drives the internal combustion engine is used alongside the electrical machine for propulsion, and on the other hand hybrid drive concepts exist in which the electrical machine is used as the starter for starting the internal combustion engine. In this way, an additional electric starter motor and the associated activating system may be dispensed with.
Compared to typical internal combustion engine drives, a hybrid drive requires a complex control device, since an internal combustion engine must be operated together with an electrical machine in order to provide the propulsion, and with a multi-layered control device for the electrical machine, since the latter is used both as a propulsion element and as a starter.
In known hybrid drives in which the electrical machine is used as the starter for the internal combustion engine, the operation of the electrical machine is monitored, and is limited or turned off when errors are detected, for safety reasons. Control systems are used according to the related art which monitor the activation, the regulation and the sensors of the electrical machine themselves and switch the electrical machine off if necessary. The electrical machine is normally switched off immediately if an error is detected.
In systems of this type, in which an error results in limited operation or in shutting down of the electrical machine, the effects of the responses to a detected error may result in the vehicle no longer being movable. In many cases, in particular if the internal combustion engine is turned off, the result of suppressing or blocking the operation of the electrical machine as a drive unit is therefore that the drive is inoperable, although the turned-off internal combustion engine is available in principle for propulsion. The control of the hybrid drive according to the related art therefore does not provide for any availability of the hybrid engine if only the electrical machine (or its sensors or control device) has an error and it has been detected.
It is therefore an object of the present invention to provide a control method and a control device for a hybrid engine which offers greater availability of the hybrid drive even in the event of an error.